1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device including forming an impurity diffusion layer in a surface of a semiconductor substrate.
2. Description of the Related Art
As transistors have been patterned finer in order to improve the performance of LSIs, the gate length has been decreased. To cope with a decrease in gate length, it is necessary to reduce a junction depth (diffusion depth) of a source/drain region. In the case of fine-patterned transistor having a gate length of 30 nm or less, its minimum junction depth is 15 nm or less, so that very shallow source/drain region is required.
According to the reported conventional ion implantation methods, an acceleration energy of 200 to 500 eV/B+ ion has been used to implant B+ or BF2+ or an acceleration energy of 1 keV or less has been used to implant As+. By these ion implantation methods, the distribution of dopant such as B or As implanted into a silicon substrate will spread. Accordingly, it is difficult to obtain the source/drain regions having a high concentration dopant distribution in which the depth is 15 nm or less and the lateral diffusion of the dopant from a mask edge to a region directly under the mask is 10 nm or less.
Moreover, point defect such as atomic vacancy or interstitial atom formed in the silicon substrate owing to the ion implantation will accelerate the diffusion of the dopant. Therefore, the source/drain region will spread more due to annealing carried out after the ion implantation for the purpose of activation of the dopant and recovery of crystal defect (damage).
To solve this problem, a method that instantaneously supplies energy necessary for the annealing has been examined. Specifically, an annealing method using a flash lamp filled with rare gas such as xenon, an annealing method using light such as infrared light or visible light, or an annealing method using laser of ultraviolet has been examined.
A flash lamp is capable of emitting light having a pulse width of sub-millimeters at the minimum. Therefore, according to the flash lamp annealing method, it is possible to activate the dopant implanted into the surface of the silicon substrate with almost no change of the dopant distribution (see T. Ito et al., Paper No. S4-3, Ext. Abs. the 5th international Workshop on Junction Technology 2005).
However, the conventional flash lamp annealing method has the following problems.
To sufficiently recover crystal defect (damage) caused by the ion implantation, a large irradiation energy of at least 30 J/cm2 is required. Such a large irradiation energy increases heat stress in the silicon substrate, thus the crystal damage such as slip or dislocation in the silicon substrate is brought about. As a result, a production yield will be lowered.
Here, in order to reduce the irradiation energy, a method is proposed, which includes ion implantation using an element in the IV group element such as Ge for pre-amorphizing the surface of the silicon substrate wherein light absorption factor of the surface of the silicon substrate is increased by the ion implantation.
However, the conventional pre-amorphization method has the following problem.
Due to the annealing performed after the pre-amorphization, crystal defect (damage) caused by the ion implantation using the element in the IV group element such as Ge is tend to remain. Such crystal defect will be a factor of increasing pn junction leakage current or off current of transistor.
On the other hand, in the case of the flash lamp method or the laser annealing method is used, if the crystal defect (damage) caused by the ion implantation is sufficiently recovered, a Si surface layer of a part of device pattern melts, thus the fine pattern of Si and SiO2 is deformed.